Topic sentence. This should appear early in the paragraph and is often but not always the first sentence. It should clearly state the main point that you are making in the paragraph. When you are planning essays, writing down a list of your topic sentences is an excellent way to check that your argument flows well from one point to the next.
You can create an essay or story outline with topic sentences, by listing in order the topic sentence of each paragraph. Once the topic sentence outline has been planned, theoretically, the hard part is done and the story should flow from there.